This disclosure is based upon, and claims priority from, French Patent Application No. 97/03630, filed Mar. 25, 1997, and International Application No. PCT/FR98/00383, filed Feb. 27, 1998, the contents of which are incorporated herein by reference.
The present invention concerns the making of smart cards, and more particularly smart cards which are capable of contactless operation by means of an antenna integrated in the card.
Smart cards are intended to carry out various operations, such as, for example, banking operations, telephone communications, identification operations, operations of debiting or recharging account units, and all sorts of operations which can be performed remotely by high-frequency electromagnetic coupling between a transmitting/receiving terminal and a card placed in the operational area of this terminal.
One of the main technical problems that is necessary to solve in the making of such cards is the connection of the antenna with the integrated circuit chip which provides the electronic functioning of the card. The conventional constraints of mechanical strength, reliability and manufacturing cost must obviously be taken into account in the manufacturing operations.
The object of the invention is to provide a manufacturing method which makes it possible to best solve the problem of the electrical connection between the chip and the antenna.
To this end, the invention proposes to make, in a first phase, an integrated circuit chip provided with at least one portion of conductive wire soldered on the chip, this wire having a part projecting with respect to the surface of the chip, and then, in a second phase, to place the chip and an antenna conductor in electrical contact, by applying the projecting part on to one end of the antenna conductor so as to establish a direct electrical contact between the antenna and the soldered wire.
In other words, use is made of the highly conventional technique of wire bonding, or soldering a wire by thermocompression, i.e., soldering a wire (in general of gold or aluminium) on a chip, but instead of using this technique in the usual way, by making a wire come from a contact pad of the chip in order to bring it to a contact pad of a chip support element (usually a connection grid or a printed circuit module), one end of the wire is soldered on a contact pad of the chip but the other end is not soldered on an external element on to which the chip would be transferred. The wire remains free in order to serve as a contact element projecting above the chip.
The invention consequently proposes a method for making a contactless smart card, having an integrated circuit chip and an antenna, characterised in that, in a preliminary step, at least one conductive wire is soldered on a contact pad of the chip without furthermore soldering it on a chip support element, and, in a subsequent step, a direct electrical contact is established between the soldered wire and one end of an antenna conductor.
Various implementations of this method can be envisaged. In a first embodiment, the first end of the soldered wire is soldered on a contact pad of the chip and the second remains free, so that the inherent elasticity of the wire facilitates the wire and the antenna being brought into contact. In another embodiment, the wire is soldered on two contact pads of the chip, and the part of the wire situated between these two pads projects above the chip. Here again, the elasticity of the wire facilitates contact with the antenna conductor. In a third embodiment, the wire is cut off very short above the chip, so that there remains in practice only a flattened metal ball on the contact pad (that is to say the ball conventionally formed by the soldering head of the thermocompression soldering apparatus), but this ball projects sufficiently to allow a contact with the antenna conductor.
The operation of soldering the conductive wire is performed preferably while the chip is still part of a wafer which will subsequently be diced (whereas the conventional wire bonding technique for connecting with an external support is always used on a chip already cut from the wafer and ready to be mounted in a package).